This invention relates to cured polyimides, and in particular crosslinked polyimides, derived from diamines comprising pendent fluorenyl groups, and comprising an aromatic ring having at least one C1-C10 branched or unbranched alkyl substituent, wherein said alkyl substituent includes a benzylic hydrogen.
U.S. Pat. No. 5,386,002 describes alkyl-substituted fluorenyl diamine-derived polyimides as thermoplastics, specifically defined therein as having the characteristic that they do not crosslink. (col. 6, lns. 1-5).
U.S. Pat. No. 3,758,434 teaches that a fluorenyl imide without alkyl substituents is soluble in xe2x80x9chot dimethyl formamidexe2x80x9d after heating to 280xc2x0 C. for 45 min. (Example 4, col. 8, lns. 28-44).
U.S. Pat. Nos. 5,750,641 and 5,969,088 describe polyimides comprising pendent fluorenyl groups and their use as an angularity enhancement layer in a liquid crystal display or as a dielectric layer in an electrical device.
U.S. Pat. No. 6,084,053 describes electronic parts made with fluorenyl polyimides. The ""053 reference does not teach that polyimides may be crosslinked and does not draw distinctions in that regard between alkyl-substituted fluorenyl diamine derived polyimides and others.
U.S. Pat. No. 5,145,942 describes crosslinking of polyimides containing methyl-substituted aromatic rings joined by carbonyl and ether groups. The ""942 reference nowhere describes a polyimide derived from a fluorenyl diamine.
Briefly, the present invention provides a cured polyimide comprising diamines comprising pendent fluorenyl groups and comprising aromatic rings having at least one C1-C10 branched or unbranched alkyl substituent, wherein said alkyl substituent includes a benzylic hydrogen. Preferably the alkyl subtitutent is methyl or ethyl, more preferably methyl. Preferably the fluorenyl diamine excludes ether linkages and more preferably excludes both ether and carbonyl-containing linkages.
In another aspect, the present invention provides a cured polyimide made by a process comprising the step of curing diamines comprising pendent fluorenyl groups and comprising aromatic rings having at least one C1-C10 branched or unbranched alkyl substituent, wherein said alkyl substituent includes a benzylic hydrogen. Preferably the step of curing is accomplished by thermal curing, preferably by raising the temperature of said polyimide to a temperature greater than 300xc2x0 C.
In another aspect, the present invention provides a crosslinked polyimide comprising diamines comprising pendent fluorenyl groups and comprising aromatic rings having at least one C1-C10 branched or unbranched alkyl substituent, wherein said alkyl substituent includes a benzylic hydrogen. Preferably the alkyl subtitutent is methyl or ethyl, more preferably methyl. Preferably the fluorenyl diamine excludes ether linkages and more preferably excludes both ether and carbonyl-containing linkages.
In another aspect, the present invention provides a crosslinked polyimide made by a process comprising the step of crosslinking diamines comprising pendent fluorenyl groups and comprising aromatic rings having at least one C1-C10 branched or unbranched alkyl substituent, wherein said alkyl substituent includes a benzylic hydrogen. Preferably the step of crosslinking is accomplished by thermal curing, preferably by raising the temperature of said polyimide to a temperature greater than the Tg of the polyimide.
What has not been described in the art, and is provided by the present invention, is curing or crosslinking of a polyimide containing diamines comprising pendent fluorenyl groups.
In this application:
xe2x80x9ccuredxe2x80x9d describes a thermally treated polymer having less solubility at a given temperature than the same polymer prior to treatment, preferably measured in regard to solvents methyl ethyl ketone, N-methylpyrrolidone or xcex3-butyrolactone and preferably at room temperature;
xe2x80x9ccrosslinkedxe2x80x9d describes a polymer having a network structure, typically demonstrated by insolublility even at elevated temperatures and for extended times;
xe2x80x9cbenzylic hydrogenxe2x80x9d refers to a hydrogen atom attached to a carbon atom directly attached to an aromatic ring, e.g., any of the three methyl hydrogens of toluene, any of the two alpha hydrogens of ethyl benzene, etc.;
xe2x80x9cpolyimidexe2x80x9d refers to a polyimide polymer unless indicated otherwise;
xe2x80x9ca polyimide comprising a diaminexe2x80x9d and like phrases should be understood to refer to polyimide polymers incorporating segments derived from the indicated diamine monomers, as by a polymerization including said monomers;
xe2x80x9cdiamines comprising pendent fluorenyl groupsxe2x80x9d refers to fluorenyl compounds disubstituted at the 9 position with amine-containing substituents, such as 9,9-bis(aminoaryl)fluorenes;
xe2x80x9cpolyimides comprising pendent fluorenyl groupsxe2x80x9d refers to polyimides derived at least in part from pendent-fluorenyl diamine monomers;
xe2x80x9cC(number)xe2x80x9d refers to a chemical moiety containing the indicated number of carbon atoms; and
the term xe2x80x9csubstitutedxe2x80x9d used without reference to a particular substituent means, for a chemical species, substituted by conventional substituents which do not interfere with the desired product or process, e.g., substituents can be alkyl, alkoxy, aryl, phenyl, halo (F, Cl, Br, I), cyano, etc.
It is an advantage of the present invention to provide a material having the optical and electrical characteristics of pendent-fluorenyl polyimides in a crosslinked and insoluble form. It is an added advantage to provide a method of casting a polyimide comprising pendant fluorenyl groups, e.g. as a film, and thereafter rendering it insoluble.